In general, an image reproduction apparatus reproduce images on an image-carrying medium by transferring toner or developer to the medium in relation to a given image. Such transfer is typically achieved through the use of a developing unit which places toner or developer on the image-carrying medium via a photoreceptor drum. To accomplish image transfer, the photoreceptor drum surface is first prepared by an electrophotographic image process to selectively accept toner in relation to the image. The developing unit then applies toner onto the photoreceptor drum via a developing roller. Toner representing the desired image on the photoreceptor drum is transferred onto an image-carrying medium such as paper. Further processing of the paper, for example, the application of heat, serves to permanently adhere the toner to the paper.
In recent years, rotary developing apparatus having multiple developing units have been proposed for color copiers, color printers and other image-forming apparatus as disclosed, for example, in U.S. Pat. Nos. 4,782,360, 4,792,825, 5,258,819, and Japanese Laid Open Publication 4-10070. In general, multiple independent developing units are housed in the rotary developing apparatus. Each of the multiple developing units are positioned around a cylindrical housing of the rotary developing apparatus and independently applies toner of a different color to a photoreceptor drum. To apply toner, only one independent developing unit is juxtaposed to the photoreceptor drum at a given time. Thus, for example, if four colors such as yellow, magenta, cyan and black are used, a developing unit containing one of these colors is rotatably positioned to juxtapose the photoreceptor drum to apply toner of the particular color according to a desired image.
Toner is selectively applied onto the photoreceptor drum across a gap between the drum and a developing roller. Toner is uniformly applied to the developing roller in a developing unit. The amount of toner on the developing roller is regulated by a doctor blade. Toner is assisted to apply onto the photoreceptor drum surface by carriers. If the gap is not maintained at a predetermined distance, an optimal amount of toner will not be transferred onto the photoreceptor drum surface. Thus, for accurate image production, a relatively constant gap distance is crucial.
Despite an initial factory adjustment, many conventional image reproducing apparatus did not correctly maintain the gap during shipping or after extended use. To maintain accurate image reproduction, the gap must be periodically adjusted. In the past, the gap was adjusted by moving the developing apparatus with respect to the photoreceptor drum. However, this form of gap adjustment creates particular problems for rotary-type developing apparatus.
As described above, rotary developing apparatus house multiple developing units which rotate about a single axis. Due to this construction, if the position of the rotary apparatus is moved with respect to a photoreceptor drum, the gap distance will change for all developing units. Thus, in the past, this type of gross gap adjustment did not provide fine gap adjustment for each developing unit. In addition, this prior gap adjustment technique did not accommodate various kinds of toner which may require different gap distances for optional transfer.
The current invention is directed to an apparatus and a method for providing an independent gap adjustment for each developing unit in a rotary developing apparatus. In addition, the solution provided by the current invention also improves the assembly process as well as the maintenance process of a rotary developing apparatus.